Is Mandibular Fossa Morphology and Articular Eminence Inclination Associated with Temporomandibular Dysfunction?

STATEMENT OF THE PROBLEM
Finding a significant relationship between temporomandibular joint (TMJ) morphology and the incidence of temporomandibular dysfunction (TMD) may help early prediction and prevention of these problems.


PURPOSE
The purpose of the present study was to determine the morphology of mandibular fossa and the articular eminence inclination in patients with TMD and in control group using cone beam computed tomography (CBCT).


MATERIALS AND METHOD
The CBCT data of bilateral TMJs of 40 patients with TMD and 23 symptom-free cases were evaluated. The articular eminence inclination, as well as the glenoid fossa depth and width of the mandibular fossa were measured. The paired t-test was used to compare these values between two groups.


RESULTS
The articular eminence inclination and glenoid fossa width and depth were significantly higher in patients with TMD than in the control group (p < 0.05).


CONCLUSION
The articular eminence inclination was steeper in patients with TMD than in the control group. Glenoid fossa width and depth were higher in patients with TMD than that in the control group. This information may shed light on the relationship between TMJ morphology and the incidence of TMD.


Introduction
Temporomandibular joint dysfunction (TMD) is one of the most prevalent pathologies which may cause orofacial pain of non-dental origin. [1] The high prevalence of TMD makes it necessary to promote diagnostic and treatment methods. [2] TMD has different etiologies which are not yet known well. [3] Articular eminence morphology has been discussed as an etiologic factor for TMD in many studies. [4][5][6][7][8] There are various diagnostic imaging techniques for the evaluation of temporomandibular joint (TMJ) structures. However, computerized tomography (CT) and cone beam computed tomography (CBCT) are the primary techniques of choice for optimal imaging of the osseous components. Although CT is widely used as a diagnostic tool in medicine, its application in dentistry is limited. [9] CBCT has a high dimensional accuracy in measuring maxillofacial structures including TMJ. [4,7,[10][11] Therefore, CBCT was employed for the evaluation of TMJ morphology in the current study.

Statistical analyses
The data analysis was conducted with the SPSS software version 17. The results of the first and second series of measurements were compared by paired t-test at a significance level of 0.05. The Student's t-test was used to determine the possible statistically significant differences between the two groups according to gender. The Student's t-test was used to determine the differences in the eminence inclination and the glenoid fossa depth and width between the patient and control groups according to their gender. P value≤ 0.05 was considered statistically significant.

Results
In There were statistically significant differences between the patient and control groups in the articular eminence inclination (p= 0.001), and also the glenoid fossa depth (p= 0.008) and width (p< 0.001). All of these three values were higher in patients with TMD than in the control group (Table 3).  The eminence inclination values of males were lesser than those of females in both patient and control groups; however, these differences were not statistically significant (Table 4).
While males and females in patient group did not differ significantly in terms of the glenoid fossa depth values, there were statistically significant differences in the control group (p= 0.047), which showed higher values in males (Table 4).
No statistically significant difference was detected between the two genders in the glenoid fossa depth values in the control group; whereas, there was statistically significant difference in the patient group (p= 0.014) with males presenting higher values (Table 4).   The inclination of articular eminence is described as the angle between the posterior wall of articular eminence and any horizontal plan. [29] It differs interindividually and determines the condylar path during mandibular functions. [30] Association between the articular eminence inclination and many other factors such as age, [31] gender, [7,27] TMD or internal derangement, [3,8] malocclusion [32] and tooth loss [30] has been investigated in different studies. In the present study, we investigated the association between the The articular eminence inclination was found to be steeper in the patient group than in control group.
A number of investigations [3,17] found that the steepness of the articular eminence might not have a predisposing effect on the development of TMD.
Sülün et al. [6] proposed higher articular eminence as a predisposing factor for the development of disk displacement with reduction. Alkhader et al. [33] found higher articular eminence in TMJs with osseous abnormalities than those cases without abnormalities.
Similarly, we found that fossa depth was higher in the TMD group than in control group. However, Ozkan et al. [3] proposed that eminence height might not be a predisposing factor for internal derangements of the joint. These controversies in articular eminence inclination and height could be due to differences in imaging techniques (CBCT versus MRI), methods of measurements, sample size, age range, and other differences between the populations.
Alkhader et al. [33] also proposed that fossa width was lower in TMJs with osseous abnormalities than the ones without such abnormalities. This is in contrast with our results showing higher fossa width in TMD group than in control group. This contrast could be attributed to the differences in case selection based on the inclusion and exclusion criteria. They only included patients with arthrogenic TMJ disorders; while, we included milder cases of TMD. We also set exclusion criteria such as congenital craniofacial abnormalities, fracture or pathology in TMJ [27] and any systemic diseases which might cause changes in bone morphology and consequently interfere with the results. [26] In line with some other studies, [27,[34][35] patients with any prosthetic rehabilitation or history of orthodontic treatment were not included in this study due to the probable etiological effect of these appliances on TMD. The articular eminence inclination completes its major growth by the age of 20. [36] Therefore, participants under 20 years of age were also excluded from this study.
Some studies reported a difference in articular eminence inclination or height according to gender. [7,27,30] Sümbüllü et al. [7] and Ilguy et al. [27] found that eminence inclination and height values of males were higher than those of females. Similarly, we found that eminence height (glenoid fossa depth) values of males were higher than those of females which was significant in the control group, but not in the patient group. In contrast with previous studies, this study found higher eminence inclination in females in both patient and control groups. These results confirm the sexual dimorphism which may be related to the variation of the amount of masticatory force affecting the joint according to gender. [7] Controversial results reported that the effect of gender in different studies could be due to the improper gender distribution of the patients. In our study as well as many others, [7,27] the number of females was higher than males and this may be the underlying cause of the prevalence of TMD among females, as already reported in some studies. [7] This study was subjected to some limitations such as improper distribution of the patients by gender and age. There were more females than males because of the higher incidence of TMD in females. [37] It was not certainly confirmed that the morphology is the cause or effect of TMD. Undoubtedly, additional studies with larger sample size are required to evaluate this relation and to resolve the mentioned controversy about eminence inclination. Further examinations are also necessary to be performed over a broader range of ages to find the effect of aging on TMJ; particularly the morphology of its components and the possible consequences such as TMD.

Conclusion
In conclusion, inclination of articular eminence was steeper in patients with TMD. These patients also showed higher values of glenoid fossa depth and width. This information may shed light on the relationship between TMJ morphology and the incidence of TMD.